I have two water lines running to the house. With one connected everything is fine but if I disconnect that one and use the other I have low pressure in the house. Two facts: the water pressure of the new line outside is greater than the water pressure than the first line. The reason I am switching if the water pressures varies on the first one pretty often during the day but the new line has even pressure although greater. Why would I have less pressure in the lines in the house when I connect the new line>

Why would I have less pressure in the lines in the house when I connect the new line> If the old line was galvanized then It's most likely clogged with iron oxide,(rust).
You ask the question.

What happens if water pressure too high entering house If your house pressure is above 80 PSI it will put a strain on elbos and faucets/valves. It will also cause your shower head to leak when you're filling the tub. What's your house pressure? Back to you, Tom